There are many applications in different fields using radiation of different electromagnetic spectral ranges for various purposes. Such purposes could include, but not limited to for example, writing patterns on a substrate, inspecting a surface, performing measurements and others. Relevant spectral ranges of the electromagnetic radiation may include visible light, IR, UV and X-ray radiation. Operation with radiation of some spectral ranges in many cases suffers from interaction of light with a medium through which the light beam has to propagate (e.g. air in case of Deep and Vacuum UV and X-ray). Such interaction may include different effects, such as absorption, scattering (elastic or inelastic), all resulting in that a part of the light beam intensity is lost on the beam's way to an addressed position. Accordingly, the power on the interaction spot at said addressed position is smaller than desired and at the same time unwanted secondary effects might occur (e.g. background signal, spot widening etc.).
In most applications of the kind specified the medium in the optical path of the beam is air. Air is known to transmit well in several “atmospheric windows”, such as the optical window between ˜190-1400 nm, including the visible part of the spectrum, the near IR and parts of the UV, the mid-IR window around ˜3.5-5 microns and the far-IR window around ˜8-12 microns. The atmospheric windows are defined such that the overall absorption of all gasses found in the atmosphere is low. Outside these windows specific gasses, e.g. such as Oxygen (blocking transmission below 190 nm), water vaporand Carbon dioxide have absorption bands that limit the transmission in atmosphere.
US 2005/077474, assigned to the assignee of the present application, describes optical method and system for use in processing articles by VUV radiation. This technique utilizes localizing incident VUV radiation propagation from an optical head assembly towards a processing site on the article outside the optical head assembly and localizing reflected VUV radiation propagation from said processing site towards the optical head assembly, by localizing a medium, non-absorbing with respect to VUV radiation, in within the light propagation path in the vicinity of said site outside the optical head assembly.
General Description
The present invention provides a novel apparatus and method enabling optical processing of an article while in a free space (air environment), eliminating a need for maintaining the article in a vacuum chamber during the processing. It should be understood that optical processing refers to any one of inspection, examination, monitoring, measurement, exposure and the like procedure applied to an article by irradiating it by electromagnetic radiation and detecting and analyzing the article response to said radiation.
The invention provides for localizing a radiation spot on the surface of an article, by creating specific local conditions in the vicinity of a processing site on the article's surface being irradiated (preferably around the intended interaction spot), such that the interaction of an optical beam with atmosphere in the vicinity of the processing site is reduced to an acceptable level, while keeping the article in air environment. The local condition in the vicinity of the processing site is a condition of minimized amount of ambient gases (typically air) in the vicinity of the processing site. This is achieved by creating, in the vicinity of region of interest (i.e. vicinity of the processing site), substantially static (or quasi-static) state of environment, non-absorbable for said spectral range or wavelength.
According to some embodiments of the invention, the above-described local conditions around a processing site (measurement spot) are created using injection of gas non absorbing for a spectrum used (inert gas), such that other gasses from the surrounding atmosphere are pushed out to a level that their interaction with optical beams are no longer significant. In this respect, an inert gas is any gas, which does not have a substantial absorption in the intended part of the spectrum. For the example of VUV, Nitrogen or Argon could be used to allow transmission below 190 nm where atmospheric Oxygen (O2) is absorbing. For the case of an X-ray beam, Helium could be used as the inert gas since its interaction with the radiation is minimal due to its low atomic number.
According to some other embodiments of the invention, the above-defined static state conditions are created by discharging (pumping) ambient gas(es) from the vicinity of the region of interest.
There is thus provided, according to one broad aspect of the invention, an apparatus for use in optical processing of an article, the apparatus comprising: one or more optical windows for directing predetermined electromagnetic radiation therethrough to illuminate a region of interest and collecting radiation returned from the illuminated region; and two or more ports operable for inputting or discharging one or more gases from the vicinity of the region of interest on the article being processed to create in the vicinity of said region a substantially static state of environment non-absorbable for said electromagnetic radiation, thereby reducing amount of ambient gas in the vicinity of said region of interest and enabling optical processing of the article while maintaining it in the ambient gas environment.
According to some embodiments of the invention, the apparatus comprises a facet having a substantially planar surface formed with one or more optical windows. Inert gas (non-absorbing for radiation being used) is supplied into a gap between the planar surface carrying the optical window(s). The inert gas is supplied in two (or more) opposite gas jets which interfere (meet) at the gap region below the optical window(s), i.e. in the vicinity of the processing site, resulting in a zone of substantially increased gas pressure in the vicinity of the processing site.
Thus, the facet of the apparatus in which the planar surface with the optical window(s) is formed has at least two orifices for flowing gas therethrough into said gap between the optical window(s) and the article. The arrangement of the optical window(s) and gas inlet orifice(s) is such that the gas flow in said gap is substantially parallel to said planar surface.
The gas flowing through the gap may be discharged via at least one outlet orifice made in said facet.
The arrangement of optical window(s) and said inlet orifice(s) may be such that the gas flows through the gap and is discharged therefrom while in a substantially laminar flow.
The arrangement of the optical window(s) and the inlet orifice(s) and outlet orifice(s) made in said facet may be such that a saddle point of the gas flow is provided in the vicinity of the processing site. By this, a zone of relatively high pressure at the saddle point is provided. As indicated above, this can be achieved by arranging the inlet and outlet orifices such that the gas flow comprises gas jets flowing in opposite directions and interfering at said saddle point. In some embodiments, there are at least two inlet and at least two outlet orifices. The outlet orifices may be arranged substantially symmetrically with respect to said saddle point. Similarly, the inlet orifices are arranged substantially symmetrically with respect to said saddle point.
As indicated above, the local conditions of low pressure or vacuum around the intended interaction spot could be created in a dynamic situation without fully evacuating the atmosphere around the whole article. This can be implemented by providing in said facet an array of spaced apart outlet orifices arranged around the optical window and operating for pumping ambient gas out of the gap between the optical window and the article, to thereby provide a zone of relatively low pressure at the vicinity of said processing site.
The outlet orifices may be arranged substantially symmetrically with respect to the optical window. At least some of the orifices are preferably arranged along one or more concentric closed-loop paths centered about said optical window.
In all the above-described embodiments, (injection or vacuum), a distance between the optical window to the article is preferably minimized in order to minimize the interaction path length between the beam and the atmosphere. This can be achieved by allowing movement of the planar surface carrying the optical window along an axis perpendicular to said planar surface. To this end, a flexure associated with the planar surface can be used, being configured and operable to enable said movement of the optical window along.
According to another broad aspect of the invention, there is provided an apparatus for use in optical processing of an article, the apparatus comprising: one or more optical windows for directing predetermined electromagnetic radiation therethrough towards a region of interest and collecting light returned from the illuminated region; and two or more ports for inputting gas, non-absorbable for said radiation towards the region of interest on the article being processed, thereby enabling creation of a substantially static state of environment non-absorbable for said radiation in the vicinity of said region of interest thus reducing amount of ambient gas in the vicinity of said region of interest and enabling optical processing of the article while maintaining it in the ambient gas environment.
In yet another broad aspect of the invention, there is provided an apparatus for use in optical processing of an article, the apparatus comprising: one or more optical windows for directing predetermined electromagnetic radiation therethrough towards a region of interest and collecting light returned from the illuminated region; and two or more ports for discharging ambient gas from the vicinity of the region of interest on the article being processed, thereby enabling creation of a substantially static state of environment non-absorbable for said radiation in the vicinity of said region of interest thus reducing amount of the ambient gas in said region of interest and enabling optical processing of the article while maintaining it in the ambient gas environment.
According to yet further aspect of the invention, there is provided an apparatus for use in optical processing of an article, the apparatus comprising: one or more optical windows for directing predetermined electromagnetic radiation therethrough towards a region of interest and collecting light returned from the illuminated region; and one or more ports operable for inputting or discharging gas from the vicinity of the region of interest on the article being processed, said one or more optical windows being mounted for controllable movement along an axis substantially perpendicular to a plane defined by the optical window.
The invention also provides a method for use in optical processing of an article, the method comprising maintaining an article under processing in ambient gas environment while creating local environmental conditions in a vicinity of a processing site of the article, said local conditions being characterized by substantially static state of environment, non-absorbable for predetermined electromagnetic radiation, in the vicinity of said processing site.